Ohm's law calculator

Calculate voltage, current or resistance with Ohm's law, plus the circuit power.

Voltage

12 V

Power24 W

Fill in the two known values according to what you chose to calculate.

How the calculation works

Ohm's law relates voltage, current and resistance: V = R × I, giving I = V/R and R = V/I. Power is P = V × I.

What is 1 ohm?

It is the resistance that lets 1 ampere flow under 1 volt.

How to remember the formula?

The VIR triangle: V on top, I and R below. Cover what you want: V = I×R, I = V/R, R = V/I.

How to find power?

P = V × I (watts). You can also use P = I²×R or P = V²/R.

Combine resistors in series or parallel to get the circuit's equivalent resistance.

Convert joules, calories, kcal, Wh, kWh and BTU.

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Updated on June 18, 2026 · by Rafael Rossi · Methodology & sources